01 - Preheat oven to 350°F. Line two baking sheets with parchment paper.
02 - Beat softened butter and sugar in a large bowl until light and fluffy.
03 - Mix in egg, lemon juice, lemon zest, and vanilla extract until well combined.
04 - Whisk together flour, baking soda, salt, and poppy seeds in a separate bowl.
05 - Gradually add dry ingredients to wet mixture, mixing until just combined.
06 - Drop rounded tablespoons of dough onto prepared baking sheets, spacing 2 inches apart.
07 - Bake for 10-12 minutes until edges are lightly golden.
08 - Let cookies rest on pan for 2 minutes, then transfer to wire rack to cool completely.
09 - Whisk powdered sugar with lemon juice until smooth. Drizzle over cooled cookies and allow to set.